Lower olefins (e.g., ethylene and propylene) are important basic raw materials in the petrochemical industries and demand for lower olefins is expected to be steadily increased in the coming years. At present, lower olefins have been produced mainly by steam cracking of naphtha. However, this process, which is non-catalytic, requires high temperatures between 800° C. and 900° C. for cracking, resulting in a large amount of energy consumption.
In this technique, the main product is ethylene, while propylene is a by-product (the gravimetric ratios of ethylene to propylene are ca. 2.0). Therefore, propylene supply by this technique might be insufficient due to the expansion of propylene demand. From these viewpoints, an energy-saving alternative process for producing propylene with high yield from the naphtha feedstock has been intensively desired.
Recently, research and development has been actively conducted for catalytic cracking processes of naphtha using zeolite-based solid acid catalysts, typified by ZSM-5 (Al-MFI zeolite).
For example, it has been proposed that a zeolite-based solid acid catalyst be produced by a process including subjecting a mixture of raw materials containing ZSM-5, a layered compound such as bentonite, silicon dioxide, phosphorus pentoxide, aluminum oxide, and boron oxide, to a crosslinking reaction in water to form an aqueous slurry containing a crosslinked product, and then forming the aqueous slurry into pellets as a solid acid catalyst (see, for example, Patent Literature 1). It is also proposed that this solid acid catalyst be used to produce ethylene and propylene as light olefins, for example, from full-range naphtha.